Joely Marie Maak, Daniel Birgel, Joachim Reitner, Eberhard Gischler, Wolf-Christian Dullo, William J. Foster, Jörn Peckmann
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引用次数: 0
Abstract
Microbial carbonates are common components of Quaternary tropical coral reefs. Previous studies revealed that sulfate-reducing bacteria trigger microbial carbonate precipitation in supposedly cryptic reef environments. Here, using petrography, lipid biomarker analysis, and stable isotope data, we aim to understand the formation mechanism of microbial carbonate enclosed in deep fore reef limestones from Mayotte and Mohéli, Comoro Islands, which differ from other reefal microbial carbonates in that they contain less microbial carbonate and are dominated by numerous sponges. To discern sponge-derived lipids from lipids enclosed in microbial carbonate, lipid biomarker inventories of diverse sponges from the Mayotte and Mohéli reef systems were examined. Abundant peloidal, laminated, and clotted textures point to a microbial origin of the authigenic carbonates, which is supported by ample amounts of mono-O-alkyl glycerol monoethers (MAGEs) and terminally branched fatty acids; both groups of compounds are attributed to sulfate-reducing bacteria. Sponges revealed a greater variety of alkyl chains in MAGEs, including new, previously unknown, mid-chain monomethyl- and dimethyl-branched MAGEs, suggesting a diverse community of sulfate reducers different from the sulfate-reducers favoring microbialite formation. Aside from biomarkers specific for sulfate-reducing bacteria, lipids attributed to demosponges (i.e., demospongic acids) are also present in some of the sponges and the reefal carbonates. Fatty acids attributed to demosponges show a higher diversity and a higher proportion in microbial carbonate compared to sponge tissue. Such pattern reflects significant taphonomic bias associated with the preservation of demospongic acids, with preservation apparently favored by carbonate authigenesis.
期刊介绍:
The journal is open to papers dealing with the interpretation of ancient and modern biotopes and carbonate depositional environments by means of facies analysis in its broadest sense. Once the central part of research in hydrocarbon exploration, facies analysis more and more integrates modern and ancient biogeological processes of a changing earth. Special emphasis is laid on paleobiology and -ecology, basin evolution, sedimentology including diagenesis and geochemistry, as well as studies emphasising the impact of life on earth history. The main part of the target group will be people in academia.